JP2012083219A - Distance sensor and distance image sensor - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a distance sensor and a distance image sensor capable of achieving high speed transfer of electrical charge while improving sensitivity.SOLUTION: A photo-gate electrode PG is a rectangular shape where a planar shape has a first and a second long sides LS1 and LS2 facing each other in a first direction and a first and a second short sides SS1 and SS2 facing each other in a second direction. A plurality of semiconductor areas FD1 and FD2 are arranged to face on both sides of the photo-gate electrode PG and to be spatially separated from each other along the second direction. An area immediately below the photo-gate electrode PG includes first areas CG1 located between the semiconductor areas FD1 and FD2 facing in the first direction and second areas CG2 sandwiched between the first areas CG1 in the second direction. Third semiconductor areas SR1 are arranged in the second areas CG2. The third semiconductor areas SR1 enhance potential in the second areas CG2 more than potential in the first areas CG1.

Description

  The present invention relates to a distance sensor and a distance image sensor.

  A conventional active optical distance measuring sensor irradiates light from a light source for light projection such as an LED (Light Emitting Diode), and detects reflected light from the object with a light detection element. It is known to output a signal corresponding to the distance up to. A PSD (Position Sensitive Detector) is known as an optical triangulation type optical distance measuring sensor that can easily measure the distance to an object, but in recent years, in order to perform more precise distance measurement, The development of TOF (Time-Of-Flight) type optical ranging sensor is expected.

  Image sensors that can simultaneously acquire distance information and image information with the same chip are required for in-vehicle use, factory automatic manufacturing systems, and the like. If an image sensor is installed in front of the vehicle, it is expected to be used for detection / recognition of the vehicle ahead and detection / recognition of pedestrians. Apart from image information, an image sensor that acquires a distance image composed of a single distance information or a plurality of distance information is also expected. It is preferable to use the TOF method for such a distance measuring sensor.

  The TOF method emits pulsed light from a light source for projection toward an object, and detects the pulsed light reflected by the object with a light detection element, thereby making the time difference between the emission timing of the pulsed light and the detection timing. Is measuring. This time difference (Δt) is the time required for the pulsed light to fly at the speed of light (= c) twice as much as the distance d to the object (2 × d), so d = (c × Δt) / 2 is established. The time difference (Δt) can be rephrased as the phase difference between the emission pulse from the light source and the detection pulse. If this phase difference is detected, the distance d to the object can be obtained.

  The charge distribution type image sensor has attracted attention as a light detection element for performing distance measurement by the TOF method. That is, in the charge distribution type image sensor, for example, the charge generated in the image sensor in response to the incident detection pulse is distributed in one potential well during the ON period of the emission pulse, and OFF. Distribute to the other potential well during the period. In this case, the ratio of the amount of charge distributed to the left and right is proportional to the phase difference between the detection pulse and the emission pulse, that is, the time required for the pulsed light to fly at the speed of light over twice the distance to the object. It will be. Various methods can be considered as the charge distribution method.

  Patent Document 1 discloses a charge generation region in which charges are generated according to incident light, a pair of signal charge collection regions that are spatially separated and collect signal charges from the charge generation region, and signal charge collection There is disclosed a TOF type distance sensor (distance image sensor) provided with a transfer electrode provided in each region and provided with a charge transfer signal having a different phase.

International Publication No. 2007/119626 Pamphlet

  By the way, as the planar shape of the charge generation region, the areas of the charge generation region are increased so as to increase the sensitivity, and the charge transfer speed in the opposite direction of the signal charge collection region is increased. A rectangular shape having first and second long sides and first and second short sides facing each other may be employed. In this case, the signal charge collection region is disposed so as to face each other with the charge generation region sandwiched in the opposing direction of the first and second long sides.

  However, when the plane shape of the charge generation region is the above rectangular shape and the signal charge collection region is arranged so as to face each other with the charge generation region sandwiched in the opposing direction of the first and second long sides, the following is performed. It has been newly found that there is a fear of causing problems.

  In the opposing direction of the first and second long sides, the electric field generated by the transfer electrode and the signal charge collection region acts, so that charges generated in the charge generation region can be transferred at high speed. In the opposing direction of the two short sides, the electric field due to the transfer electrode and the signal charge collecting region does not sufficiently act, and in particular, it is difficult to transfer charges generated near the first and second short sides of the charge generation region at high speed. It becomes.

By extending the signal charge collection region and the transfer electrode in the opposing direction of the first and second short sides, respectively, charges generated near the first and second short sides of the charge generation region can be transferred at high speed. Become. However, if the area of the signal charge collection region is increased by extending the signal charge collection region in the opposing direction of the first and second short sides, the sensitivity of the distance sensor is lowered for the following reason. The charge (Q) transferred to the signal charge collection region causes a voltage change (ΔV) represented by the following relational expression by the electrostatic capacity (Cfd) of the signal charge collection region.
ΔV = Q / Cfd
As the area of the signal charge collection region increases, the capacitance of the signal charge collection region also increases, and the generated voltage change becomes smaller. That is, the charge-voltage conversion gain is lowered. For this reason, the sensitivity of a distance sensor will fall.

  As described above, in order to increase the sensitivity of the distance sensor, the area of the signal charge collection region must be reduced, and the length of the signal charge collection region in the opposing direction of the first and second short sides. Is required to be set shorter than the length of the charge generation region in the opposing direction of the first and second short sides. Therefore, even if the transfer electrode is extended in the opposing direction of the first and second short sides, it is difficult to transfer charges in the opposing direction of the first and second short sides in the region immediately below the transfer electrode. The problem that the charge transfer rate is low cannot be solved.

  An object of the present invention is to provide a distance sensor and a distance image sensor that can realize high-speed transfer of charges while achieving high sensitivity.

  The distance sensor according to the present invention generates a charge in response to incident light and has a rectangular shape having first and second long sides opposed to each other and first and second short sides opposed to each other in plan view. A certain charge generation region and a first direction in which the first long side and the second long side are opposed to each other across the charge generation region, and a second direction in which the first short side and the second short side are opposed to each other. The plurality of signal charge collection regions that are spaced apart from each other and collect signal charges from the charge generation region, and are arranged between the signal charge collection region and the charge generation region, respectively, and charge transfer in different phases The second electrode of the charge generation region is disposed in a second region sandwiched in the second direction between the first regions located between the transfer electrode to which a signal is applied and the charge collection region opposed in the first direction in the charge generation region. The potential in the region is the potential in the first region. Characterized in that it and a potential adjusting means for increasing than.

  In the distance sensor according to the present invention, the potential in the second region of the charge generation region is higher than the potential in the first region by the potential adjusting means. For this reason, the charge generated near the second region of the charge generation region easily moves in the second direction toward the first region due to the difference in potential. The charges that have moved in the second direction toward the first region of the charge generation region are transferred at high speed by the electric field generated by the transfer electrode and the signal charge collection region. Therefore, the charge generation region is increased in area by setting the length in the direction (second direction) orthogonal to the facing direction to be longer than the length in the facing direction (first direction) of the signal charge collection region. That is, even when the sensitivity is increased by making the plane shape of the charge generation region the above rectangular shape and setting the area of the signal charge collection region small, it occurs in the charge generation region. The charged charges can be transferred at high speed.

  The potential adjusting means may be a semiconductor region having the same conductivity type as the charge generation region and having a higher impurity concentration than the charge generation region. In this case, since the impurity concentration of the semiconductor region disposed opposite to the charge generation region in the second direction is higher than that of the charge generation region, the potential level difference can be increased. Since the semiconductor region can be formed by adjusting the impurity concentration, the potential adjusting means can be easily realized.

  A photogate electrode disposed on the charge generation region may be further provided, and the potential adjusting means may be an electrode to which a potential lower than the potential applied to the photogate electrode is applied. In this case, since the potential applied to the electrodes arranged opposite to each other across the charge generation region in the second direction is lower than the potential applied to the photogate electrode, the potential difference in potential can be increased. With a simple configuration such as an electrode, the potential adjusting means can be easily realized.

  The distance image sensor according to the present invention includes an imaging region composed of a plurality of units arranged in a one-dimensional shape or a two-dimensional shape on a semiconductor substrate, and obtains a distance image based on a charge amount output from the unit. In the image sensor, one unit is the distance sensor. In the present invention, as described above, even when a high sensitivity is achieved by setting the planar shape of the charge generation region to the rectangular shape and setting the area of the signal charge collection region to be small, Charges generated in the charge generation region can be transferred at high speed.

  According to the present invention, it is possible to provide a distance sensor and a distance image sensor that can realize high-speed transfer of charges while achieving high sensitivity.

It is explanatory drawing which shows the structure of the distance measuring device which concerns on this embodiment. It is a figure for demonstrating the cross-sectional structure of a distance image sensor. It is a schematic plan view of a distance image sensor. It is a schematic diagram for demonstrating the structure of the pixel of a distance image sensor. It is a figure which shows the cross-sectional structure along the VV line in FIG. It is a figure which shows the cross-sectional structure along the VI-VI line in FIG. It is a figure which shows potential distribution for demonstrating the accumulation | storage operation | movement of a signal charge. It is a figure which shows potential distribution for demonstrating the accumulation | storage operation | movement of a signal charge. It is a schematic diagram for demonstrating the structure of a pixel. It is a timing chart of various signals. It is a schematic diagram for demonstrating the structure of the pixel in the modification of a distance image sensor. It is a figure which shows the cross-sectional structure along the XII-XII line | wire in FIG. It is a schematic diagram for demonstrating the structure of a pixel. It is a timing chart of various signals. It is a figure which shows potential distribution for demonstrating the accumulation | storage operation | movement of a signal charge. It is a schematic diagram for demonstrating the structure of the pixel in the modification of a distance image sensor. It is a schematic diagram for demonstrating the structure of the pixel in the modification of a distance image sensor. It is a schematic diagram for demonstrating the structure of the pixel in the modification of a distance image sensor. It is a schematic diagram for demonstrating the structure of the pixel in the modification of a distance image sensor. It is a schematic diagram for demonstrating the structure of the pixel in the modification of a distance image sensor. It is a schematic diagram for demonstrating the structure of the pixel in the modification of a distance image sensor.

  Hereinafter, preferred embodiments of the present invention will be described in detail with reference to the accompanying drawings. In the description, the same reference numerals are used for the same elements or elements having the same function, and redundant description is omitted.

  FIG. 1 is an explanatory diagram showing the configuration of the distance measuring apparatus.

The distance measuring device, a distance image sensor 1, a light source 3 for emitting near-infrared light, a driving circuit 4 to be supplied to the light source 3 a pulse drive signal S _P, first included in each pixel of the range image sensor 1 and a second gate electrode (TX1, TX2: see FIG. 4), the pulsed driving signal _S and the control circuit 2 to provide a detection gate signals _S 1, _{S 2} in synchronization with the _P, the distance the first and second image sensors 1 An arithmetic circuit 5 is provided that calculates a distance from a signal d ′ (m, n) indicating distance information read from the semiconductor region (FD1 to FD2: see FIG. 4) to an object H such as a pedestrian. . The distance in the horizontal direction D from the distance image sensor 1 to the object H is defined as d.

The control circuit 2 is input to the pulse drive signal S _P to the switch 4b of the driving circuit 4. A light projecting light source 3 comprising an LED or a laser diode is connected to a power source 4a via a switch 4b. Therefore, when the pulse drive signal S _P is input to the switch 4b, a drive current having the same waveform as the pulse drive signal S _P is supplied to the light source 3, the pulse light L _P as a probe light for distance measurement from the light source 3 Is output.

When the pulse light L _P is irradiated on the object H, the pulse light is reflected by the object H, the pulse light L _D, the distance is incident on the image sensor 1 outputs a pulse detection signal S _D.

  The distance image sensor 1 is fixed on the wiring board 10, and a signal d ′ (m, n) having distance information is output from each pixel via the wiring on the wiring board 10.

The waveform of the pulse drive signal S _P, a square wave of period T, the high level "1", when the low level is "0", the voltage V (t) is given by the following equation.
・ Pulse drive signal S _P :
V (t) = 1 (provided that 0 <t <(T / 2))
V (t) = 0 (provided that (T / 2) <t <T)
V (t + T) = V (t)

The waveforms of the detection gate signals S ₁ and S ₂ are square waves having a period T, and the voltage V (t) is given by the following equation.
・ Detection gate signal S ₁ :
V (t) = 1 (provided that 0 <t <(T / 2))
V (t) = 0 (provided that (T / 2) <t <T)
V (t + T) = V (t)
Detection gate signal S ₂ (= inversion of S ₁ ):
V (t) = 0 (provided that 0 <t <(T / 2))
V (t) = 1 (provided that (T / 2) <t <T)
V (t + T) = V (t)

The pulse signal _{S P, S 1, S 2} , S D , it is assumed that has all pulse period 2 × _{T P.} Detection gate signal S ₁ and the pulse detection signal S _D are both the amount of charge generated by the distance image sensor within 1 when "1" Q1, the detection gate signal S ₂ and the pulse detection signal S _D are both "1" In this case, the amount of charge generated in the distance image sensor 1 is Q2.

The phase difference between _one detection gate signal S ₁ and the pulse detection signal _{SD in} the distance image sensor 1 is the distance in the overlap period when the other detection gate signal S ₂ and the pulse detection signal _SD are “1”. It is proportional to the amount of charge Q2 generated in the image sensor 1. That is, the charge amount Q2 is the charge amount for the period logical product of the detection gate signal S ₂ and the pulse detection signal S _D is "1". The total charge quantity generated in one pixel is Q1 + Q2, when the pulse width of the half cycle of the drive signal _{S P} and _{T P, Δt = T P ×} Q2 / (Q1 + Q2) long enough, with respect to the drive signal _{S P} The pulse detection signal _SD is delayed. The flight time Δt of one pulsed light is given by Δt = 2d / c, where d is the distance to the object and c is the speed of light. Therefore, a signal d ′ (m, n) having distance information from a specific pixel. two charge amount as) (Q1, Q2) when is outputted, the arithmetic circuit 5, a charge amount Q1, Q2 input, based on the half cycle pulse width T _P that is known in advance, the object H Distance d = (c × Δt) / 2 = c × T _P × Q2 / (2 × (Q1 + Q2)) is calculated.

  As described above, if the charge amounts Q1 and Q2 are read out separately, the arithmetic circuit 5 can calculate the distance d. The above-described pulse is repeatedly emitted, and the integrated value can be output as the respective charge amounts Q1 and Q2.

  The ratio of the charge amounts Q1 and Q2 to the total charge amount corresponds to the above-described phase difference, that is, the distance to the object H. The arithmetic circuit 5 calculates the distance to the object H according to this phase difference. As described above, when the time difference corresponding to the phase difference is Δt, the distance d is preferably given by d = (c × Δt) / 2, but an appropriate correction operation may be added to this. . For example, when the actual distance and the calculated distance d are different, a coefficient β for correcting the latter is obtained in advance, and the product after shipping is obtained by multiplying the calculated distance d by the coefficient β. The calculation distance d may be used. When the outside air temperature is measured and the light speed c varies depending on the outside air temperature, the distance calculation can be performed after performing the calculation for correcting the light speed c. The relationship between the signal input to the arithmetic circuit and the actual distance may be stored in advance in the memory, and the distance may be calculated by a lookup table method. The calculation method can also be changed depending on the sensor structure, and a conventionally known calculation method can be used for this.

  FIG. 2 is a diagram for explaining a cross-sectional configuration of the distance image sensor.

The distance image sensor 1 is a surface incident type distance image sensor and includes a semiconductor substrate 1A. The range image sensor 1, a pulse light L _D from the light incident surface 1FT of the semiconductor substrate 1A is incident. The back surface 1BK opposite to the light incident surface 1FT of the distance image sensor 1 is connected to the wiring substrate 10 via the adhesion region AD. The adhesion region AD has an insulating adhesive or filler. The distance image sensor 1 includes a light shielding layer LI having an opening formed at a predetermined position. The light shielding layer LI is disposed in front of the light incident surface 1FT.

  FIG. 3 is a schematic plan view of the distance image sensor.

  In the distance image sensor 1, the semiconductor substrate 1A has an imaging region 1B composed of a plurality of pixels P (m, n) arranged in a two-dimensional manner. From each pixel P (m, n), two charge amounts (Q1, Q2) are output as the signal d '(m, n) having the above-described distance information. Each pixel P (m, n) outputs a signal d '(m, n) corresponding to the distance to the object H as a minute distance measuring sensor. Therefore, if the reflected light from the object H is imaged on the imaging region 1B, a distance image of the object as a collection of distance information to each point on the object H can be obtained. One pixel P (m, n) functions as one distance sensor.

  FIG. 4 is a schematic diagram for explaining the configuration of the pixels of the distance image sensor. FIG. 5 is a diagram showing a cross-sectional configuration along the line VV in FIG. FIG. 6 is a diagram showing a cross-sectional configuration along the line VI-VI in FIG. In FIG. 4, the conductor 11 is not shown.

The distance image sensor 1 includes a semiconductor substrate 1A having a light incident surface 1FT and a back surface 1BK facing each other. The semiconductor substrate 1A includes a p-type first substrate region 1Aa located on the back surface 1BK side, and a p ⁻ -type second substrate region 1Ab located on the light incident surface 1FT side and having an impurity concentration lower than that of the first substrate region 1Aa. And consist of The semiconductor substrate 1A can be obtained, for example, by growing a p ⁻ type epitaxial layer having an impurity concentration lower than that of the semiconductor substrate on the p type semiconductor substrate.

In each pixel P (m, n), the distance image sensor 1 includes a plurality of photogate electrodes PG and a plurality (three in the present embodiment) of first and second gate electrodes TX1 and TX2, respectively. In the embodiment, three (first) and second semiconductor regions FD1, FD2 and a plurality (two in the present embodiment) of third semiconductor regions SR1 are provided. The photogate electrode PG is provided on the light incident surface 1FT via the insulating layer 1E. Each of the first and second gate electrodes TX1, TX2 is provided adjacent to the photogate electrode PG via the insulating layer 1E on the light incident surface 1FT. Each of the first and second semiconductor regions FD1 and FD2 accumulates charge flowing into a region immediately below the corresponding gate electrode TX1 and TX2. The third semiconductor region SR1 has a conductivity type opposite to that of the first and second semiconductor regions FD1, FD2. The semiconductor substrate 1A of the present embodiment is made of Si, the insulating layer 1E is made of SiO _2.

  The photogate electrode PG has a rectangular shape having first and second long sides LS1, LS2 facing each other and first and second short sides SS1, SS2 facing each other. In the present embodiment, the ratio between the lengths of the first and second long sides LS1, LS2 and the lengths of the first and second short sides SS1, SS2 is set to, for example, about 1: 2 to 1:15. The photogate electrode PG is made of polysilicon, but other materials may be used.

  A region corresponding to the photogate electrode PG in the semiconductor substrate 1A (a region immediately below the photogate electrode PG) functions as a charge generation region in which charges are generated according to incident light. Therefore, the charge generation region has a planar shape corresponding to the photogate electrode PG, that is, a rectangular shape having first and second long sides facing each other and first and second short sides facing each other.

  The first semiconductor regions FD1 are arranged spatially separated from each other along the first long side LS1 on the first long side LS1 side of the photogate electrode PG. The second semiconductor regions FD2 are arranged spatially separated from each other along the second long side LS2 on the second long side LS2 side of the photogate electrode PG. The first semiconductor region FD1 and the second semiconductor region FD2 face each other across the photogate electrode PG in the facing direction of the first and second long sides LS1, LS2. The first and second semiconductor regions FD1, FD2 have a rectangular shape in plan view. The ratio of the length of the first and second semiconductor regions FD1, FD2 in the opposing direction of the first and second short sides SS1, SS2 to the length of the first and second short sides SS1, SS2 is, for example, 1: It is set to about 0.5 to 1: 2. In the present embodiment, the first and second semiconductor regions FD1, FD2 have a square shape. The first and second semiconductor regions FD1, FD2 function as signal charge collection regions.

  A region (charge generation region) immediately below the photogate electrode PG includes a plurality (three in this embodiment) of first regions CG1 and a plurality (two in this embodiment) of second regions CG2. Contains. The first region CG1 is located between the first and second semiconductor regions FD1, FD2 facing each other in the facing direction of the first and second long sides LS1, LS2. The second region CG2 is sandwiched between the first regions CG1 in the opposing direction of the first and second short sides SS1, SS2.

  The first gate electrode TX1 is provided between the photogate electrode PG and the first semiconductor region FD1. The second gate electrode TX2 is provided between the photogate electrode PG and the second semiconductor region FD2. The first and second gate electrodes TX1, TX2 have a rectangular shape in plan view. In the present embodiment, the first and second gate electrodes TX1, TX2 have a rectangular shape in which the opposing direction of the first and second short sides SS1, SS2 is the long side direction. The long side direction of the first and second gate electrodes TX1, TX2, that is, the length of the photogate electrode PG in the opposing direction of the first and second short sides SS1, SS2, and the first and second gate electrodes TX1, TX2 The ratio with the length in the short side direction is set to, for example, about 1: 2 to 1:15. The first and second gate electrodes TX1 and TX2 are made of polysilicon, but other materials may be used. The first and second gate electrodes TX1, TX2 function as transfer electrodes.

  The third semiconductor region SR1 is disposed in the second region CG2 in the region (charge generation region) immediately below the photogate electrode PG. The third semiconductor region SR1 is disposed to face the first region CG1 across the first region CG1 in the facing direction of the first and second short sides SS1, SS2. The third semiconductor region SR1 has a rectangular shape in plan view. The third semiconductor region SR1 is provided between the first short side SS1 and the second short side SS2. In the present embodiment, the third semiconductor region SR1 has a rectangular shape in which the opposing direction of the first and second long sides LS1, LS2 is the long side direction.

  The first and second semiconductor regions FD1, FD2 are regions made of an n-type semiconductor having a high impurity concentration, and are floating diffusion regions. The third semiconductor region SR1 is a region having the same conductivity type as the semiconductor substrate 1A and having a higher impurity concentration than the semiconductor substrate 1A, that is, a high impurity concentration p-type semiconductor. The third semiconductor region SR1 may be a p-type well region or a p-type diffusion region.

The thickness / impurity concentration of each region is as follows.
First substrate region 1Aa of the semiconductor substrate 1A: thickness 5 to 700 μm / impurity concentration 1 × 10 ¹⁸ to 10 ²⁰ cm ⁻³
Second substrate region 1Ab of the semiconductor substrate 1A: thickness 3 to 30 μm / impurity concentration 1 × 10 ¹³ to 10 ¹⁶ cm ⁻³
First and second semiconductor regions FD1, FD2: thickness 0.1 to 0.4 μm / impurity concentration 1 × 10 ¹⁸ to 10 ²⁰ cm ⁻³
Third semiconductor region SR1: thickness 1 to 5 μm / impurity concentration 1 × 10 ¹⁶ to 10 ¹⁸ cm ⁻³

  The insulating layer 1E is provided with contact holes for exposing the surfaces of the first and second semiconductor regions FD1, FD2. A conductor 11 for connecting the first and second semiconductor regions FD1, FD2 to the outside is disposed in the contact hole.

  An opening LIa is formed in the light shielding layer LI at a position corresponding to the photogate electrode PG. Therefore, light enters the semiconductor substrate 1A (a region immediately below the photogate electrode PG) through the opening LIa of the light shielding layer LI. The region where the first and second semiconductor regions FD1 and FD2 are disposed in the semiconductor substrate 1A is covered with the light shielding layer LI to prevent light from entering the first and second semiconductor regions FD1 and FD2. Yes. As a result, it is possible to prevent generation of unnecessary charges due to light incident on the first and second semiconductor regions FD1, FD2. The light shielding layer LI is made of, for example, a metal (metal) such as aluminum.

  When a high level signal (positive potential) is applied to the first and second gate electrodes TX1 and TX2, the potential below the first and second gate electrodes TX1 and TX2 is directly below the photogate electrode PG in the semiconductor substrate 1A. Lower with respect to the potential of the region. As a result, negative charges (electrons) are drawn in the direction of the first and second gate electrodes TX1, TX2, and accumulated in the potential well formed by the first and second semiconductor regions FD1, FD2. An n-type semiconductor includes a positively ionized donor, has a positive potential, and attracts electrons. When a low level signal (ground potential) is applied to the first and second gate electrodes TX1 and TX2, a potential barrier is generated by the first and second gate electrodes TX1 and TX2. Therefore, the charge generated in the semiconductor substrate 1A is not drawn into the first and second semiconductor regions FD1, FD2.

  In the distance image sensor 1, charges generated in the deep part of the semiconductor in response to the incidence of light for projection are drawn into a potential well provided on the light incident surface 1FT side, thereby enabling accurate measurement at high speed.

Pulse light L _D from the object incident from the light incident surface 1FT of the semiconductor substrate 1A leads to the region immediately below the photogate electrode PG provided on the surface side of the semiconductor substrate 1A. The charges generated in the semiconductor substrate 1A with the incidence of the pulsed light are distributed from the region immediately below the photogate electrode PG to the region immediately below the first and second gate electrodes TX1 and TX2 adjacent thereto. That is, the detection gate signal _S 1, _{S 2} in synchronization with the drive signal _{S P} output light source to the first and second gate electrodes TX1, TX2, via the wiring board 10, given alternating, the photo gate electrode PG Charges generated in the region immediately below flow into regions immediately below the first and second gate electrodes TX1 and TX2, respectively, and flow into the first and second semiconductor regions FD1 and FD2.

The ratio of the charge amounts Q1 and Q2 accumulated in the first semiconductor region FD1 or the second semiconductor region FD2 to the total charge amount (Q1 + Q2) is the emission pulse light emitted by applying the drive signal _SP to the light source, and This corresponds to the phase difference of the detection pulse light that has returned by reflecting the outgoing pulse light by the object H.

  Although not shown, the distance image sensor 1 includes a back gate semiconductor region for fixing the potential of the semiconductor substrate 1A to a reference potential.

  7 and 8 are diagrams showing a potential distribution in the vicinity of the light incident surface 1FT of the semiconductor substrate 1A for explaining the signal charge accumulation operation. 7 and 8, the downward direction is the positive direction of the potential.

Due to the potential applied to the photogate electrode PG at the time of light incidence (a potential intermediate between the higher potential and the lower potential applied to the first and second gate electrodes TX1 and TX2), The potential φ _PG of the region is set slightly higher than the substrate potential. The figure shows the potential φ _TX1 in the region immediately below the first gate electrode TX1, the potential φ _TX2 in the region immediately below the second gate electrode TX2, the potential φ _FD1 in the first semiconductor region _FD1 , and the potential of the second semiconductor region FD2. The potential φ _FD2 is shown.

High potential of the detection gate signals S ₁ is inputted to the first gate electrode TX1, as shown in FIG. 7 (a), charges generated immediately below the photogate electrode PG, according to the potential gradient, Accumulation is performed in the potential well of the first semiconductor region FD1 via the region immediately below the first gate electrode TX1. The charge amount Q1 is accumulated in the potential well of the first semiconductor region FD1.

At this time, as shown in FIG. 8, by arranging the third semiconductor region SR1, the potential φPG of the region immediately below the photogate electrode _PG is increased on the second region CG2 side. Therefore, a potential gradient that decreases from the second region CG2 side toward the first region CG1 side is formed in the region immediately below the photogate electrode PG in the opposing direction of the first and second short sides SS1, SS2. ing.

  The charges generated near the second region CG2 in the region immediately below the photogate electrode PG are accelerated according to the potential gradient formed by the third semiconductor region SR1, and move quickly toward the first region CG1. Then, as described above, the transferred electric charge passes through the region immediately below the first gate electrode TX1 according to the potential gradient formed by the electric field of the first gate electrode TX1 and the first semiconductor region FD1. Accumulated in the potential well of one semiconductor region FD1.

Following the detection gate signal S _1, the high potential of the detection gate signal S ₂ is inputted to the second gate electrode TX2, as shown in FIG. 7 (b), immediately below the photogate electrode PG The generated charges are accumulated in the potential well of the second semiconductor region FD2 via the region immediately below the second gate electrode TX2 according to the potential gradient. The charge amount Q2 is accumulated in the potential well of the second semiconductor region FD2.

Also at this time, as shown in FIG. 8, the third semiconductor region SR1 is arranged, so that the potential φPG in the region immediately below the photogate electrode _PG is increased on the second region CG2 side. Therefore, a potential gradient that decreases from the second region CG2 side toward the first region CG1 is formed in the region immediately below the photogate electrode PG in the opposing direction of the first and second short sides SS1, SS2. Yes.

  The charges generated near the second region CG2 in the region immediately below the photogate electrode PG are accelerated according to the potential gradient formed by the third semiconductor region SR1, and move quickly toward the first region CG1. Then, as described above, the transferred electric charge passes through the region immediately below the second gate electrode TX2 according to the potential gradient formed by the electric field of the second gate electrode TX2 and the second semiconductor region FD2. 2 accumulated in the potential well of the semiconductor region FD2.

  FIG. 9 is a schematic diagram for explaining a configuration of a pixel.

The first gate electrode TX1, the detection gate signals _{S 1} supplied. The second gate electrode TX2, the detection gate signal _{S 2} is applied. That is, charge transfer signals having different phases are applied to the first gate electrode TX1 and the second gate electrode TX2.

Charges generated in the area immediately below the photogate electrode PG, when the detection gate signals S ₁ at a high level to the first gate electrode TX1 is given, the potential well constituted by first semiconductor region FD1 It flows as signal charge. The signal charges accumulated in the first semiconductor region FD1 is read from the first semiconductor region FD1 as an output corresponding to the accumulated charge amount _{Q 1 (V out1).} Charges generated in the area immediately below the photogate electrode PG, when the second gate electrode TX2 detection gate signal S ₂ of the high level is given, the potential well formed by the second semiconductor region FD2 It flows as signal charge. The signal charges accumulated in the second semiconductor region FD2 is read from the second semiconductor region FD2 as an output corresponding to the accumulated charge amount _{Q 2 (V out2).} These outputs (V _out1 , V _out2 ) correspond to the signal d ′ (m, n) described above.

  FIG. 10 is a timing chart of actual various signals.

The one-frame period _TF includes a signal charge accumulation period (accumulation period) T _acc and a signal charge read period (readout period) _Tro . Focusing on one pixel, the accumulation period T _acc, the signal based on the pulse drive signal S _P with a plurality of pulses are applied to the light source, in synchronization with this, the detection gate signal S _1, S ₂ mutually The first and second gate electrodes TX1 and TX2 are applied in reverse phase. Prior to the distance measurement, the reset signal reset is applied to the first and second semiconductor regions FD1 and FD2, and the charges accumulated inside are discharged to the outside. In this example, after the reset signal reset is turned on for a moment and then turned off, a plurality of drive vibration pulses are sequentially applied, and further, charge transfer is sequentially performed in synchronization with the first and second semiconductors. Signal charges are accumulated and accumulated in the regions FD1 and FD2. Then, in the readout period _{T ro,} the signal charge accumulated in the first and second semiconductor regions FD1, the FD2 is read.

  When distributing charges, a positive high-level detection signal is normally applied to one of the first gate electrode TX1 and the second gate electrode TX2 (for example, the first gate electrode TX1). At the same time, the other gate electrode (for example, the second gate electrode TX2) is supplied with detection signals having a phase difference of 180 degrees. At this time, when a detection signal applied to the other gate electrode (for example, the second gate electrode TX2) is applied at a lower level (for example, the ground potential), the potential immediately below the second gate electrode TX2 increases, A mountain is formed. Thereby, it becomes difficult for the electric charge to flow from the photogate electrode PG side to the second semiconductor region FD2, and generation of unnecessary noise components can be suppressed.

  As described above, in the present embodiment, the planar shape of the photogate electrode PG is set to a rectangular shape. Thereby, the area of the region (charge generation region) immediately below the photogate electrode PG is increased to increase the sensitivity of the distance image sensor 1, and the charge transfer rate in the first and second semiconductor regions FD1, FD2 is increased. Can be increased.

In the present embodiment, the first and second semiconductor regions FD1 and FD2 have a length in the opposing direction of the first and second short sides SS1 and SS2, and the first and second short sides SS1 of the photogate electrode PG. , SS2 is set to be extremely smaller than the length in the opposing direction, and the areas of the first and second semiconductor regions FD1, FD2 are also set to be smaller than the area of the photogate electrode PG. For this reason, the area of the first and second semiconductor regions FD1, FD2 is smaller than the area of the region where charges can be transferred to the first and second semiconductor regions FD1, FD2 in the region (charge generation region) immediately below the photogate electrode PG. The area is greatly reduced. The charges (charge amounts Q1, Q2) transferred to and accumulated in the first and second semiconductor regions FD1, FD2 are expressed by the following relational expression according to the capacitances (Cfd) of the first and second semiconductor regions FD1, FD2. A voltage change (ΔV) indicated by
ΔV = Q1 / Cfd
ΔV = Q2 / Cfd
Therefore, when the areas of the first and second semiconductor regions FD1 and FD2 are reduced, the capacitance (Cfd) of the first and second semiconductor regions FD1 and FD2 is also reduced, and the generated voltage change (ΔV) is large. Become. That is, the charge voltage conversion gain is increased. Also from this, the sensitivity of the distance image sensor 1 can be increased.

  By the way, in the present embodiment, the potential on the second region CG2 side of the region (charge generation region) immediately below the photogate electrode PG is higher than the potential in the first region CG1 by the third semiconductor region SR1. Thus, a potential gradient lowered toward the first region CG1 is formed. For this reason, the charges generated near the second region CG2 in the region immediately below the photogate electrode PG are directed in the opposing direction of the first and second short sides SS1 and SS2 toward the first region CG1 due to the potential gradient. It becomes easy to move. The charges that have moved from the second region CG2 side toward the first region CG1 in the opposing direction of the first and second short sides SS1 and SS2 are the electric field generated by the first gate electrode TX1 and the first semiconductor region FD1, or the first Transfer is performed at high speed by the electric field generated by the two-gate electrode TX2 and the second semiconductor region FD2. Therefore, by setting the planar shape of the photogate electrode PG (charge generation region) to a rectangular shape, the area is increased, and by setting the areas of the first and second semiconductor regions FD1, FD2 to be extremely small, Even when the sensitivity is increased, charges generated in the region immediately below the photogate electrode PG can be transferred at high speed.

  In the present embodiment, the third semiconductor region SR1 is formed by adjusting the impurity concentration of the semiconductor substrate 1A. For this reason, the structure for raising the potential on the second region CG2 side in the region immediately below the photogate electrode PG to be higher than the potential in the first region CG1 can be easily realized.

  Next, a modified example of the distance image sensor 1 will be described with reference to FIGS. 11 and 12. FIG. 11 is a schematic diagram for explaining a pixel configuration in a modified example of the distance image sensor. FIG. 12 is a diagram showing a cross-sectional configuration along the line XII-XII in FIG. The present modification is different from the above embodiment in that a potential adjustment electrode EL is provided instead of the third semiconductor region SR1. In FIG. 11, the conductor 11 is not shown.

  The distance image sensor 1 includes a plurality of photogate electrodes PG and a plurality (three in this modification) of first and second gate electrodes TX1 and TX2 in each pixel P (m, n). In the modification, three (first) and second semiconductor regions FD1, FD2 and a plurality (two in the present modification) of potential adjustment electrodes EL are provided. The potential adjustment electrode EL is provided adjacent to the photogate electrode PG via the insulating layer 1E on the light incident surface 1FT.

  In the present modification, as in the above-described embodiment, the charge generation region has a rectangular shape having first and second long sides that face each other and first and second short sides that face each other. Yes. The charge generation region includes a plurality (three in the present embodiment) of first regions CG1 and a plurality (two in the present embodiment) of second regions CG2.

  The potential adjustment electrode EL is disposed on the second region CG2 of the charge generation region. The potential adjustment electrode EL is disposed so as to oppose the first region CG1 across the first and second short sides of the charge generation region. The potential adjustment electrode EL has a rectangular shape in plan view. In the present embodiment, the potential adjustment electrode EL has a rectangular shape in which the opposing direction of the first and second long sides of the charge generation region is the long side direction. The ratio of the length of the potential adjustment electrode EL in the opposing direction of the first and second long sides of the charge generation region to the length of the potential adjustment electrode EL in the opposing direction of the first and second short sides of the charge generation region is For example, it is set to about 1: 2 to 1:15. The potential adjustment electrode EL is made of polysilicon, but other materials may be used.

  The potential adjustment electrode EL is provided between the first short side and the second short side of the charge generation region. For this reason, in the present modification, the photogate electrode PG is provided by being divided into a plurality of parts for each first region CG1 in the region immediately below the photogate electrode PG. Since the potential adjustment electrode EL is made of polysilicon, light passes through the potential adjustment electrode EL and enters the semiconductor substrate 1A. Therefore, the region immediately below the potential adjustment electrode EL in the semiconductor substrate 1A also functions as a charge generation region.

Potential adjustment electrodes EL, as shown in FIGS. 13 and 14, the potential adjustment signal by _{S 3,} the potential applied to the photo gate electrode PG _{(P PG)} lower potential than the (first and second gate electrodes TX1 , Intermediate potential between the higher potential and the lower potential applied to TX2). FIG. 13 is a schematic diagram for explaining a configuration of a pixel. Figure 14 is a timing chart of the actual various signals, other signals except the potential adjustment signal S ₃ is the same as the signal shown in FIG. 10. The potential adjustment signal S ₃ is given from the control circuit 2.

In this modification, since the potential adjustment electrode EL is applied with a potential lower than the potential applied to the photogate electrode PG, as shown in FIG. 15, the potential φ _{PG in} the region immediately below the photogate electrode _PG. Is increased on the second region CG2 side. Therefore, a potential gradient that decreases from the second region CG2 side toward the first region CG1 is formed in the region immediately below the photogate electrode PG.

  The charges generated near the second region CG2 of the charge generation region are accelerated according to the potential gradient formed by the potential adjustment electrode EL, and quickly move toward the first region CG1. Similarly to the above-described embodiment, the transferred charges are the gradient of the potential formed by the electric field of the first gate electrode TX1 and the first semiconductor region FD1, or the electric field of the second gate electrode TX2 and the second semiconductor region FD2. Are accumulated in the potential well of the first semiconductor region FD1 or in the potential well of the second semiconductor region FD2.

  As described above, also in the present modified example, as in the above-described embodiment, the planar shape of the charge generation region is set to a rectangular shape to increase the area, and the first and second semiconductor regions FD1, FD2 By setting this area to be extremely small, the charge generated in the charge generation region can be transferred at high speed even when the sensitivity is increased.

  In the present modification, the potential on the second region CG2 side in the charge generation region is made higher than the potential in the first region CG1 by the potential adjustment electrode EL. For this reason, the structure for raising the potential on the second region CG2 side in the charge generation region to be higher than the potential in the first region CG1 can be easily realized.

  Next, a modified example of the distance image sensor 1 will be described with reference to FIGS. 16 and 17. 16 and 17 are schematic diagrams for explaining the configuration of the pixels in a modification of the distance image sensor. In the present modification, the shape of the third semiconductor region SR1 or the potential adjustment electrode EL is different from that in the above embodiment. Also in FIG.16 and FIG.17, illustration of the conductor 11 mentioned above is abbreviate | omitted.

  As shown in FIG. 16, the third semiconductor region SR1 has a circular shape in plan view. The potential adjustment electrode EL also has a circular shape in plan view as shown in FIG. Also in this modification, the potential on the second region CG2 side in the charge generation region is higher than the potential in the first region CG1.

  Next, a modified example of the distance image sensor 1 will be described with reference to FIGS. 18 and 19. 18 and 19 are schematic diagrams for explaining the configuration of the pixels in a modification of the distance image sensor. In this modification, the shapes of the first and second gate electrodes TX1, TX2 are different from those in the above embodiment. 18 and 19 also omit the illustration of the conductor 11 described above.

  As shown in FIGS. 18 and 19, the first gate electrode TX1 may extend along the first long side LS1 so as to extend over the plurality of first semiconductor regions FD1. Similarly, the second gate electrode TX2 may extend along the second long side LS2 so as to cover the plurality of second semiconductor regions FD2. As described above, the first and second gate electrodes TX1 and TX2 may be provided separately for each of the semiconductor regions FD1 and FD2, or provided integrally over the plurality of semiconductor regions FD1 and FD2. Also good.

  Next, a modified example of the distance image sensor 1 will be described with reference to FIGS. 20 and 21 are schematic diagrams for explaining the configuration of pixels in a modification of the distance image sensor. In this modification, the arrangement of the first and second semiconductor regions FD1, FD2 is different from that in the above embodiment. 20 and 21 also omit the illustration of the conductor 11 described above.

  In the modification shown in FIG. 20, the first and second semiconductor regions FD1, FD2 are spatially separated from each other along the first long side LS1 on the first long side LS1 side of the photogate electrode PG. Alternatingly arranged. Also on the second long side LS2 side of the photogate electrode PG, the first and second semiconductor regions FD1 and FD2 are spatially separated from each other and alternately arranged along the second long side LS2 of the photogate electrode PG. ing.

  In the modification shown in FIG. 21, the first and second semiconductor regions FD1 and FD2 are spatially separated from each other along the long side and alternately arranged on one long side of the charge generation region. Yes. Also on the other long side of the charge generation region, the first and second semiconductor regions FD1, FD2 are spatially separated from each other and alternately arranged along the other long side of the charge generation region.

  20 and FIG. 21, the first and second semiconductor regions FD1 and FD2 are arranged on two opposing long sides, respectively. In the manufacturing process, for example, when the photomask is displaced to one long side, the transfer of charges to the first and second semiconductor regions FD1, FD2 arranged on one long side is hindered. The amount of charge accumulated in the first and second semiconductor regions FD1 and FD2 disposed on the long side of the semiconductor device decreases. On the other hand, since charges are easily transferred to the first and second semiconductor regions FD1 and FD2 disposed on the other long side, the first and second semiconductors disposed on the other long side. The amount of charge accumulated in the regions FD1 and FD2 increases. As a result, the decrease in the amount of charge accumulated in the first and second semiconductor regions FD1 and FD2 disposed on one long side becomes the first and second semiconductor regions disposed on the other long side. The amount of charge accumulated in FD1 and FD2 is compensated for and the charge amount unbalance is offset. As described above, the modification shown in FIG. 20 and FIG. 21 has an advantageous effect that it is possible to suppress the change in characteristics with respect to the displacement of the photomask.

  The preferred embodiments of the present invention have been described above. However, the present invention is not necessarily limited to the above-described embodiments, and various modifications can be made without departing from the scope of the present invention.

  A charge generation region in which charge is generated in response to incident light may be configured by a photodiode (for example, an embedded photodiode). The distance image sensor 1 may be a back-illuminated distance image sensor. The distance image sensor 1 is not limited to the pixel P (m, n) arranged two-dimensionally, and the pixel P (m, n) may be arranged one-dimensionally.

  The number of the first and second semiconductor regions FD1, FD2 is not limited to three, but may be two as shown in FIGS. 20 and 21, or may be four or more.

  The shape of the third semiconductor region SR1 and the potential adjustment electrode EL in plan view is not limited to the rectangular shape or the circular shape described above, and may be other shapes. Further, the lengths of the third semiconductor region SR1 and the potential adjustment electrode EL in the opposing direction of the first and second long sides LS1, LS2 are not limited to the values described above. As long as the potential on the second region CG2 side in the charge generation region can be higher than the potential in the first region CG1, it may be set shorter than the length of the second short side SS1, SS2, for example. .

  INDUSTRIAL APPLICABILITY The present invention can be used for a distance sensor and a distance image sensor mounted on a product monitor or a vehicle in a factory production line.

  DESCRIPTION OF SYMBOLS 1 ... Distance image sensor, 1A ... Semiconductor substrate, 1Aa ... 1st substrate region, 1Ab ... 2nd substrate region, CG1 ... 1st region, CG2 ... 2nd region, EL ... Potential adjustment electrode, FD1 ... 1st semiconductor region, FD2 ... second semiconductor region, LS1 ... first long side, LS2 ... second long side, P ... pixel, PG ... photogate electrode, SR1 ... third semiconductor region, SS1 ... first short side, SS2 ... second short Side, TX1... First gate electrode, TX2... Second gate electrode.

Claims (4)

A charge generation region that generates a charge in response to incident light and has a rectangular shape having first and second long sides that face each other and first and second short sides that face each other;
A first direction in which the first long side and the second long side are opposed to each other across the charge generation region, and a second direction in which the first short side and the second short side are opposed to each other. A plurality of signal charge collection regions that are spaced apart from each other and collect signal charges from the charge generation region;
A transfer electrode disposed between the signal charge collection region and the charge generation region, respectively, to which a charge transfer signal having a different phase is applied;
In the second region of the charge generation region, disposed in a second region sandwiched in the second direction between the first regions located between the charge collection regions facing each other in the first direction in the charge generation region. And a potential adjusting means for increasing the potential of the first region more than the potential in the first region.   The distance sensor according to claim 1, wherein the potential adjusting unit is a semiconductor region having the same conductivity type as the charge generation region and having a higher impurity concentration than the charge generation region. A photogate electrode disposed on the charge generation region;
The distance sensor according to claim 1, wherein the potential adjusting means is an electrode to which a potential lower than a potential applied to the photogate electrode is applied. In a distance image sensor that has an imaging region composed of a plurality of units arranged one-dimensionally or two-dimensionally on a semiconductor substrate and obtains a distance image based on the amount of charge output from the unit,
One said unit is the distance sensor as described in any one of Claims 1-3, The distance image sensor characterized by the above-mentioned.

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